What affect has the Padder in a Superheterodyne?

What affect has the Padder in a Superheterodyne?

Question  from  Mr. R. S. 

I apologize for being too hasty in my request for assistance, since I am awaiting some silver-mica caps which are as closely rated to the originals as possible. If there any members who  have replaced them, 

it would be helpful to know how critical the values should be to maintain the 487kHz for the ZF.

Late, but not to late?  Answer from Mr. Knoll:

I have  calculate the SABA Circuit from the Superhet 455W Unit
See Fig. 1

When this capacity (440pF) called "Padder" ( in german: padding) , have a tolerance off +/- 2,5% the Error goes to zerro with the aligment  from L and C in the Antenna and Osc. Part off the Set, but only on the tree Points.
Between this points, a higher or lower deviation off the Intermediate Freqency  (in Kc  is to observe, see Fig.2     the  green lines shows  the deviation in Kc.

To minimice the affect on the received Signal , SABA and other europaen Manufacturer,  used  two tuned Circuits (Bandfilter). in the Antenna Input Section.  see also  http://www.radiomuseum.org/dsp_forum_post.cfm?thread_id=28228

(Hans M Knoll) --------
     
In USA,  this Condenser "Padder"  (440pf) is most used for aligment the Calibration of the Scale/ Dial.  In this case, the inductance is fixed. Earlyer (1937) Saba Models have used the same technique.

The 455W has variable  Coils on all Circuits, therefor the Cv= "Padder" (440pF) is fixed, the recommendet Value is:  nominal Value +/- 1% to 2,5%. 

Hans M. Knoll

 

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